With environmental concerns becoming one of the most important issues facing the shipping/ship-building industry today, SSPA has witnessed strong demand for the development of energy saving devices (ESD). SSPA anticipates that the demand will be greater to respond to new requirements set by the IMO regulation on energy efficient design index (EEDI). SSPA has been involved in many joint research projects in developing energy saving solutions. Daewoo Shipbuilding and Marine Engineering Co. Ltd. (DSME) has developed several ESDs in cooperation with SSPA, where SSPA has tested most of the ESDs designed by DSME over the last 10 years. The pre-swirl stator (PSS) is a device mounted on the stern boss just upstream of the propeller (see Fig. 6 or Fig. 33). It is designed to generate pre-swirl flow to the propeller in order to gain a favorable interaction with the propeller that improves the propulsive efficiency and results in a power reduction. This paper is a full description of one of the developments of PSS from the early design stage, optimization phase, and confirmation by model tests to validation through sea trial tests.